Enhanced Oil Recovery (EOR) may be used to increase oil recovery in fields worldwide. There are three main types of EOR, thermal, chemical/polymer and gas injection, which may be used to increase oil recovery from a reservoir, beyond what can be achieved by conventional means—possibly extending the life of a field and boosting the oil recovery factor.
Thermal enhanced recovery works by adding heat to the reservoir. The most widely practiced form is a steam-drive, which reduces oil viscosity so that it can flow to the producing wells. Chemical flooding increases recovery by reducing the capillary forces that trap residual oil. Polymer flooding improves the sweep efficiency of injected water. Miscible gas injection works in a similar way to chemical flooding. By injecting a fluid that is miscible with the oil, trapped residual oil can be recovered.
Oil is often withdrawn from a reservoir in a non-uniform manner. That is, most of the oil is produced from the more easily drainable sections of the formation, and relatively little oil comes from the less easily drainable sections. This is especially true in highly fractured reservoirs or those having sections of widely varying permeability wherein oil is left in the less accessible portions of the reservoir. In such reservoirs an ordinary secondary recovery flooding treatment is often of limited value, as the injected fluid tends to sweep or pass through the same sections of the formation which are susceptible to good drainage, thus either bypassing or entering to only a limited extent those sections of the formation which cannot be readily drained.
Certain liquids and gases are desirable for secondary recovery flooding treatments as they have the ability to mix with the oil in place and be produced from the formation as a mixture. Other liquids and gases are undesirable for secondary recovery flooding treatments as they do not mix with the oil in place and often finger through the formation leaving most of the oil in the formation. In certain situations, there is a gas stream containing both desirable and undesirable gases. There is a need in the art for systems and methods to separate the desirable from the undesirable gases.
Referring to FIG. 1, there is illustrated prior art system 100. System 100 includes underground formation 102, underground formation 104, underground formation 106, and underground formation 108. Production facility 110 is provided at the surface. Well 112 traverses formations 102 and 104, and terminates in formation 106. The portion of formation 106 is shown at 114. Oil and/or gas are produced from formation 106 through well 112, to production facility 110. Gas and liquid may be separated from each other, gas stored in gas storage 116 and liquid stored in liquid storage 118.
U.S. Pat. No. 5,167,280 discloses a solvent stimulation process whereby a viscosity reducing agent is circulated through a horizontal well via a production string. Said agent exits the production string and enters an annulus formed by said string and a liner. Said agent diffuses into the reservoir at a pressure below the reservoir pressure. As said agent diffuses through the reservoir under the influence of a concentration gradient, it reduces the oil's viscosity and makes it mobile. Simultaneously, oil of reduced viscosity migrates into the well under a pressure drawdown influence. A pseudo steady state production rate is achieved when convective movement of the oil of reduced viscosity is exactly counterbalanced by the diffusional rate of the viscosity reducing agent in a stimulated radial zone along said well. This stimulates a large volume of oil through the extensive surface area of the wellbore thus producing increased volumes of hydrocarbonaceous fluids from the reservoir. The viscosity reducing agent may be selected from a member of the group consisting of carbon dioxide, flu gas, carbon monoxide, helium, hydrogen, C1-C10 hydrocarbons, methanol, ethanol, toluene, carbon disulfide, and mixtures thereof. U.S. Pat. No. 5,167,280 is herein incorporated by reference in its entirety.
There are available streams of gas mixtures, for example waste streams from a chemical process or a heater, which can be used for EOR. However, these streams of gas mixtures may contain one or more gases that are desirable for EOR and one or more gases that are undesirable for EOR. There is a need in the art to separate the desirable from the undesirable gases.
There is a further need in the art for improved systems and methods for enhanced oil recovery. There is a need in the art for improved systems and methods for enhanced oil recovery with injectant mixtures. There is a need in the art for improved systems and methods for enhanced oil recovery with improved injectant mixing apparatus and methods.